Charter Communications can sue its former law firm, Irell & Manella, for malpractice, a federal district court judge ruled, despite the law firm's claim that it could not mount an effective defense. Charter was founded by Microsoft's Paul Allen, and Allen, not a party to the lawsuit, is a client of Irell. Charter alleges that because of a mistake by an Irell associate Allen ended up purchasing a different kind of security and owning a smaller-than-expected amount in another corporation, resulting in $150 million in damages. CFO.com, Green Light for Legal Malpractice Suit.